A PWS is a public warning system alerting to natural disasters or man-made accidents that may cause damages to human life and properties. A PWS service is provided by a telecom operator to a user, contents thereof may be provided by a warning message providing department. When a public warning event occurs, the warning message providing department generates a warning message and sends the same to operators. The operators use their network to send the warning message to user terminals. Since a message released by the PWS may cause a mass panic, requirements for security are very high. According to the security requirements of the PWS, a security mechanism should identify a sending source of a warning notification, thereby preventing a false warning notification, and protecting the integrity of the warning notification.
In the prior art, the sending source of the warning notification is identified via the following method, so that the false warning notification is prevented and the integrity of the warning notification is protected:
firstly, multiple global certification authorities (CAs) are deployed in the world, and public keys of these CAs are configured in a terminal;
secondly, a cell broadcast entity (CBE) obtains an implicit certificate from a CA periodically, that is, the CA issues the implicit certificate for the cell broadcast entity;
then, when a public warning event occurs, the cell broadcast entity broadcasts a message of the PWS to a warning location;
after receiving the message released by the PWS, firstly, the user terminal calculates a public key of the cell broadcast entity according to the public keys of the CAs saved locally and the implicit certificate in the message of the PWS;
and then verifies a signature of the cell broadcast entity over the message of the PWS via the public key of the cell broadcast entity, thus verifying the validity of the PWS message.
However, when multiple CAs are configured in the user terminal, after receiving the message of the PWS, since there isn't information for determining the CA in the implicit certificate, the user terminal cannot know which CA the received implicit certificate belongs to, or the user terminal does not know the public key of which CA should be used to complete verification of the PWS message. Thus, the user terminal can only try one by one, in this case, it is likely that the user terminal cannot obtain a correct key until the last one is tried, which greatly influences the timeliness of verification of the PWS message.